1. Technical Field
The present application relates to an all-solid lithium secondary battery.
2. Description of the Related Art
An all-solid lithium secondary battery in which a solid material is used as the electrolyte is safer in principle than conventional lithium secondary batteries in which a combustible liquid electrolyte is used, and can attain high energy density. Therefore, in recent years, research and development of all-solid lithium secondary batteries is being actively conducted.
An all-solid lithium secondary battery includes a positive-electrode active substance layer and a negative-electrode active substance layer, and a solid electrolyte layer interposed between these active substance layers. The positive-electrode active substance layer and the negative-electrode active substance layer both contain an active substance which is capable of occlusion and release of lithium ions. In an all-solid lithium secondary battery, with oxidation/reduction of the positive electrode and the negative electrode, lithium ions migrate in the solid electrolyte layer between the positive-electrode active substance layer and the negative-electrode active substance layer, whereby the lithium secondary battery can be charged or discharged.
An active substance occludes or releases lithium ions with charging and discharging. Therefore, the active substance expands or contracts with every charging and discharging cycle, so that stress due to expansion and contraction of the active substance occurs at the interface between the active substance layer and the solid electrolyte layer. Therefore, when charge/discharge cycles are repeated, the strength of adherence between the active substance layer and the solid electrolyte layer may decrease, thus leading to an increased interface resistance. This may cause a decrease in the battery output power. In some cases, the solid electrolyte layer may peel from the active substance layer, so that the battery may no longer function.
In answer thereto, Japanese Laid-Open Patent Publication No. 2008-226639 (hereinafter “Patent Document 1”) proposes an active substance layer which includes a plurality of electrode elements that are disposed at intervals on a solid electrolyte layer. Patent Document 1 states that this construction alleviates the stress caused by expansion and contraction of the active substance (electrode element) due to charging and discharging, and that the cycle characteristics of the all-solid lithium secondary battery can be improved.